The present invention relates to a reagent composition for measuring ionic strength or specific gravity of aqueous solution samples, a test device obtained by impregnating or coating such a reagent composition into or on a carrier, and a process for using such a reagent composition or a test device for the measurement.
The specific gravity of urine is now directly measured by processes using, a urine gravimeter, a pycnometer, a refractometer, etc. These processes almost provide necessary precision. But the apparatuses used therefor require much time and cost for correcting scales and cleaning so as to maintain the required precision, accompanied with various inconvenience. Further, a quantity of urine sample is necessary at the time of measurement, but sometimes the amount may be scant. In addition, bubbles at the liquid surface and capillarity make the readout of scales difficult.
On the other hand, there have been developed and partially put into practical use a process for measuring a change of color tone or absorbance caused by mixing urine and a reagent solution by the naked eye or a colorimeter, and a process for easily measuring a specific gravity or ionic strength of urine comprising dipping a specimen shaped into a stick form, and judging a change of color tone with the naked eye. The latter process can be carried out not only by the measurement of absorbance using a colorimeter or the naked eye judgement by a comparison of color charts, but also by the measurement of reflectance using a light emitting diode. Further, the process of using the test device has an advantage of simultaneously measuring other items of urine examination such as glucose, hemoglobin, protein, leucocyte, bilirubin, pH, ascorbic acid, urobilinogen, ketones, a nitrite, etc.
Various processes for measuring ionic strength or specific gravity of liquid samples by the measurement of changes of color tone or absorbance are disclosed as follows.
U.S. Pat. No. 4,015,462 discloses a process comprising holding microcapsules encapsulating colorants on a carrier matrix, contacting the microcapsules with a solution of low osmotic pressure to raise the inner pressure of microcapsules, to distend and rupture the microcapsules and to release the colorants, and applying a phenomenon of changing the color of matrix (the depth of color being proportional to the specific gravity of the solution).
Japanese Patent Unexamined Publication No. 55-101047 (GB 2037981) discloses a process for measuring the ionic strength or specific gravity by using a test device containing a composition comprising a polyelectrolyte such as polyacrylic acid or polyvinylamine, which is neutralized at least at about 50%, and a pH indicator.
Japanese Patent Unexamined Publication No. 56-21064 (EP 23631) discloses a process using a composition comprising a strongly acidic or strongly basic polyelectrolyte, a buffering substance capable of maintaining the pH at least about pH 5.5, and a means for indicating a pH, the polyelectrolyte being polystyrene sulfonate, polyvinyl sulfate, or polyvinylbenzyl ammonium chloride.
Japanese Patent Unexamined Publication No. 59-133207 (U.S. Pat. No. 4,473,650) discloses a reagent composition comprising a weakly basic polyelectrolyte polymer neutralized with a strong organic acid, and an indicator, said polyelectrolyte polymer being polyethyleneimine, polyvinylamine, polyaminostyrene, or a copolymer of the monomers constituting the polyelectrolyte polymer.
Japanese Patent Unexamined Publication No. 59-133208 (U.S. Pat. No. 4,532,216) discloses a composition comprising a weakly basic polyelectrolyte polymer containing at least one carboxyl group in the form of an ammonium salt and an indicator.
Japanese Patent Unexamined Publication No. 2-66451 (U.S. Pat. No. 5,106,752, U.S. Pat. No. 5,064,615) discloses a composition comprising at least one pH buffer (without a polyelectrolyte polymer) or at least one pH buffer and/or at least one complex-forming agent, and at least one pH indicator.
Japanese Patent Unexamined Publication No. 3-100461 (EP 418169) discloses a process using a dye or dye precursor wherein an ionic concentration relates to a solubility.
These processes and compositions have been developed as processes for measuring ionic strength or specific gravity of liquid samples using a test device, and partly put into practical uses. These processes measure one or more special components among Na, K, etc., which are factors of specific gravity of urine. Thus, the obtained data does not always agree to the specific gravity completely. Further, when samples with various levels of specific gravities are measured, there is a common problem in that since the color difference change of colored tone is small in a high specific gravity region, it is difficult to judge with the naked eye. In addition, according to these processes, since a coloring rate is relatively slow, it requires undesirably a long time for the measurement, when a number of samples are to be automatically judged optically.